1. Field of the Invention
The present invention relates to a plasma processing device for performing plasma arc cutting or plasma arc welding, and more particularly, to improvements to a structure for simplifying the operation of replacing consumable parts, such as electrodes, nozzles, and the like, in a plasma torch.
The present invention also relates to a plasma torch for performing cutting or welding of work by means of a plasma arc formed between an electrode and a work piece, and more particularly, to improvements in the electrical and mechanical connection structure between the electrode and torch main unit.
The present invention also relates to a plasma torch wherein the accuracy of locating the position of the nozzle and electrode is improved.
2. Description of the Related Art
In a plasma torch used for plasma arc processing, there is gradual wear of the electrode and nozzle with the passage of time during which an arc is generated. In some situations, the consumable parts thereof may be replaced several times during the course of a single day's processing work.
In order to replace the electrode and nozzle, it is of course necessary to remove the electrode and nozzle from the plasma torch, but depending on the model, it may also be necessary to remove other peripheral parts at the same time. Such peripheral parts may include, for example, insulating guides inserted between the electrode and nozzle, and one type or several types of caps, or the like, provided covering the outer side of the nozzle.
The plasma torch is fixed to a carriage provided on the upper portion of a working table, and it performs cutting or welding operations with respect to a work piece on the working table, whilst being conveyed by the carriage and moved along a programmed path of travel. When exchanging the consumable parts in the torch, usually, the torch is withdrawn to a position where the exchanging operation can be readily performed, whereupon the torch is disassembled and the consumable parts are replaced. However, since the replacing operation is carried out on the work table, this task is not necessarily easy to perform. Moreover, since it is necessary to remove and then reattach a plurality of small components during the replacing operation, care must be taken that these small components are not dropped. Furthermore, it is necessary to perform the task of reattaching components with a very great deal of caution, in order that no dust, or the like, generated by cutting, enters into the inner portion of the torch.
In order that the painstaking task of exchanging consumable parts can be carried out in a straightforward manner, plasma torches known variously as "cassette torches", "one-touch torches" or "quick-change torches" have been disclosed (Japanese Patent Application Laid-open No. 62-500085, Japanese Patent Publication No. 03-27309.) A cassette-type torch is divided into two sections : a head section comprising a torch end portion, electrode, nozzle, gas tubes, cooling water tubes, and the like, and a base section comprising a power supply cable, gas tubes, cooling water tubes, and the like, which are connected to the head section. The head section and base section are devised in such a fashion that they can be connected and separated in a straightforward manner. A plurality of head sections in which new consumable parts are installed are prepared in advance, and the consumable parts can be replaced simply, by exchanging only the head section connected to the base section. In this cassette-type torch, the replacement of consumable parts can also be automated.
In a cassette-type plasma torch, two electric current paths (for the electrode and nozzle) operating at high current and high voltage, and at least one gas passage (for the plasma gas), and feed and return water passages in a cooling water circuit, are divided into a portion on the head section side and a portion on the base section side, the connection, electrical insulation and seals between these portions being established at the dividing surfaces between the head section and the base section.
Therefore, compared to a standard conventional torch described previously, which does not have a cassette system, the cassette-type torch provides simpler replacement of consumable parts, but since the structure of the torch is more complex, it is significantly more expensive. In other words, since it is necessary to ensure satisfactory electrical insulation and sealing at the connecting surfaces of the head section and base section, in order that there are no electrical insulation faults or gas or water leaks, in addition to the operation of simply connecting and separating the head section and base section, a special structure which is not required in a standard torch must be employed, and therefore, the cost thereof increases. For example, whereas the cost of a standard torch may be 100,000 yen, the cost of a cassette-type torch having the same processing capacity may be 400,000 yen, or the like. Consequently, in practice, cassette-type torches have not become widely used.
In general, since electrodes are consumable parts and need to be replaced frequently, a sleeve-shaped electrode seating is installed inside the main unit of the torch, and the electrode is mounted detachably on the sleeve-shaped electrode seating. The electrode seating serves not only to fix the electrode mechanically, but also acts as an electrical terminal for supplying an arc current to the electrode.
In a conventional plasma torch, the electrode and seating each respectively comprise electrical connection surfaces which are perpendicular to the axis of the torch. The electrode is only able to move linearly in the direction of the torch axis, with respect to the seating. Therefore, if the electrode is installed in the seating whilst foreign matter, such as dirt or dust, is attached to the electrical connection surfaces, then the electrical connection surfaces will rise up due to this foreign matter and hence fail to fit together completely, leading to connection faults. In this case, the electrical connection surfaces will generate heat and may experience melting. There is an especially high probability of connection faults occurring in low-current types of torch which have a weak attachment force. Therefore, when installing an electrode, it is necessary to perform the painstaking task of cleaning the entire electrical connection surfaces, very carefully, by wiping the electrical connection surface of the electrode and the electrical connection surface inside the main unit of the torch, adequately, with gauze, or the like.
By the way, conventionally, various techniques have been proposed for maintaining a high degree of positioning accuracy of the nozzle and the electrode. One of these conventional techniques proposes that the nozzle and electrode are located in position in the axial direction and radial direction, by forming the inner surface of the nozzle and the outer surface of the electrode as interlocking surfaces, forming step sections in these respective interlocking surfaces, and interposing an insulating material therebetween, whilst the electrode is coupled integrally to the torch main unit by fixing the nozzle to the end portion of the torch main unit (for example, Japanese Utility Model Application Laid-Open No. 03-14077.)
According to the conventional technology described above, the smaller the clearances allowed respectively between the nozzle, electrode and insulating material, the higher the level of positioning accuracy that can be maintained. However, if the clearance gaps between the nozzle, electrode and insulating material are made too small, they will become difficult to fit together and take apart, when exchanging the nozzle or electrode, and hence the replacing operation is impeded.
For this reason, in the prior art, the clearances between these parts have been set to relatively large values, thus leading to problems in that the positioning accuracy of the nozzle and electrode declines as a consequence.
On the other hand, it has also been proposed that the nozzle, electrode and insulating material are fabricated as an integrated part, thereby dramatically improving the positioning accuracy of the nozzle and the electrode.
However, if an integrated part is used in this way, the whole part must be replaced, even if only one of the nozzle or the electrode has come to the end of its life, whilst the other is still in a usable state. Moreover, since the insulating material, which is not a consumable item, is also replaced at the same time, there is an increase in running costs.
Therefore, it is an object of the present invention to enable consumable parts to be replaced in a simple fashion, whilst avoiding increased complexity in the structure of a plasma torch and increased costs for same.
It is a further object of the present invention to simplify the task of installing an electrode, whilst avoiding connection faults between electrical connection surfaces due to foreign matter.
It is yet a further object of the present invention to resolve the problems of the prior art described above, by adopting a composition wherein a nozzle and an electrode can be replaced independently, whilst the positioning accuracy of the nozzle and electrode is improved.